全文获取类型
收费全文 | 3355篇 |
免费 | 113篇 |
国内免费 | 8篇 |
专业分类
化学 | 2670篇 |
晶体学 | 24篇 |
力学 | 39篇 |
综合类 | 1篇 |
数学 | 139篇 |
物理学 | 603篇 |
出版年
2023年 | 21篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 54篇 |
2019年 | 54篇 |
2018年 | 38篇 |
2017年 | 25篇 |
2016年 | 57篇 |
2015年 | 83篇 |
2014年 | 96篇 |
2013年 | 159篇 |
2012年 | 217篇 |
2011年 | 230篇 |
2010年 | 121篇 |
2009年 | 121篇 |
2008年 | 241篇 |
2007年 | 245篇 |
2006年 | 231篇 |
2005年 | 209篇 |
2004年 | 165篇 |
2003年 | 130篇 |
2002年 | 121篇 |
2001年 | 67篇 |
2000年 | 54篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 17篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 39篇 |
1984年 | 24篇 |
1983年 | 16篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 25篇 |
1973年 | 19篇 |
排序方式: 共有3476条查询结果,搜索用时 0 毫秒
991.
Kazuo Soga Satoru Hosoda Sakuji Ikeda 《Journal of polymer science. Part A, Polymer chemistry》1974,12(4):729-736
Copolymerizations of carbon dioxide and N-phenylethylenimine were carried out with the use of various catalysts and solvents. The infrared spectrum of the polymer produced showed the characteristic absorption peak at 1730–1735 cm?1 based on the urethane linkage. The content of the urethane linkage decreased in the following order: Mn(acac)2 ≈ MnCl24H2O > Al(OBu)3 > Ti(OBu)4 > ZnCl2 ? BF3OEt2 = VCl3 = Mn(acac)3 = FeCl3 = CrCl3 · 6H2O = 0. The manganase (bivalent) catalyst in combination with n-hexane solvent was found to be the best system for the copolymerization, and this system received detailed study. Generally speaking, both the polymer yield and the content of the urethane linkage increased with increasing content of carbon dioxide in the feed as well as with increasing polymerization temperature. From the fractionation of polymer in methanol, it was found that the produced polymer is composed of both homopolymer of N-phenylethylenimine and copolymer of N-phenylethylenimine and carbon dioxide. The content of the urethane linkage of the copolymer thus fractionated was as high as about 80%. 相似文献
992.
Yoshizaki M Matsushita S Fujiwara Y Ikeda T Ono M Nohara T 《Chemical & pharmaceutical bulletin》2005,53(7):839-840
Two novel sapogenols, isoesculeogenin A (1) and esculeogenin B (2) of steroidal alkaloid glycosides, lycoperoside F and esculeoside B, respectively, isolated from the ripe tomato have been characterized as (5alpha,22R,23R,25S)-3beta,23,27-trihydroxyspirosolane and (5alpha,22S,23R,25S)-22,26-epimino-16beta,23-epoxy-3beta,23,27-trihydroxycholestane, respectively. 相似文献
993.
Kap Ku Kang Jae Kwon Oh Young‐Tae Jeong Takesh Shiono Tomiki Ikeda 《Macromolecular rapid communications》1999,20(6):308-311
Monocyclopentadienyl compounds, CpMCl3 (M = Ti, Zr) supported on activated MgCl2 were used for the polymerizations of ethylene in the presence of methylaluminoxane (MAO) or a common alkylaluminium as a cocatalyst. By supporting CpMCl3 on MgCl2, the catalyst activity was increased drastically to show high activity similar to MgCl2‐supported TiCl4 catalysts. The activity of the CpZrCl3 /MgCl2 catalyst was higher than that of the CpTiCl3/MgCl2 one. Both catalysts gave polymers with high molecular weight (Mw) and broad molecular weight distribution (Mw/Mn) in comparison with the corresponding soluble half‐metallocene catalysts. 相似文献
994.
Daisuke Sawai Akira Yamane Hiroshi Takahashi Tetsuo Kanamoto Masayoshi Ito Roger S. Porter 《Journal of Polymer Science.Polymer Physics》1998,36(4):629-640
Ultradrawing of atactic poly(acrylonitrile) (PAN) was investigated for a Mv series, ranging 8.0 × 104–2.3 × 106. Samples for the draw were prepared from 0.5–30 wt % solutions of PAN in N,N′-dimethylformamide. The solutions were converted to a gel by quenching from 100 to 0°C. The dried gel films were initially drawn uniaxially by solid-state coextrusion (first-stage draw) to an extrusion draw ratio (EDR) of 16, followed by further tensile draw at 100–250°C (second-stage draw). The maximum total draw ratio (DRt,max) and tensile properties achieved by two-stage draw increased remarkably with sample Mv. Other factors affecting ductility were the solution concentration from which gel was made and the second-stage draw temperature. The effects of these variables became more prominent with increasing Mv. The temperature for optimum second-stage draw increased with sample Mv. Both the initial gel and the drawn products showed no small-angle X-ray long period scattering maximum, suggesting the absence of a chain-folded lamellae structure, which had been found in our previous study on the drawing of nascent PAN powder. The chain orientation function (fc) and sample density (ρs) increased rapidly with DRt in the lower range (DRt < 30) and approached constant values of fc = 0.980–0.996 and ρs = 1.177–1.181 g/cm3, respectively, at higher DRt > 30–100. The tensile modulus also showed a similar increase with DRt. The tensile strength increased linearly with DRt, reaching a maximum, and decreased slightly at yet higher DRt. The highest modulus of 28.5 GPa and strength of 1.6 GPa were achieved with the highest Mv of 2.3 × 106. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 629–640, 1998 相似文献
995.
996.
997.
998.
999.
1000.
Kazuoki Ikeda 《Algebra Colloquium》2000,7(3):329-333
The aim of this paper is to describe simple methods to distribute the ordinary irreducible characters of finite groups into p-blocks and calculate the other character values from part of the values of the ordinary irreducible characters for p-blocks.2000 Mathematics Subject Classification: 20C20 相似文献